Floodback happens when the evaporator is fed more refrigerant than it can boil off: low indoor airflow, a dirty coil, an overfeeding or stuck-open expansion valve, overcharge on a fixed orifice, or very light load. Superheat drops to zero and the suction line, accumulator and even the compressor shell sweat or frost. The liquid dilutes oil and washes bearings, wearing out compressors quietly.
Zero superheat and the compressor shell is sweating, it's flooding back, check the blower before touching the charge.
Also heard as
- flood back
- flooding back
- liquid floodback
Related terms
Slugging
Liquid refrigerant or oil being drawn into a compressor's cylinders, where it can't be compressed and causes damage.
Superheat
How many degrees refrigerant vapor is above its boiling point at the pressure it is at.
Accumulator
A tank in the suction line that catches liquid refrigerant before it can reach and damage the compressor.
TXV
Thermostatic expansion valve: a metering device that adjusts refrigerant flow to hold constant evaporator superheat.